I have a 3 cyl volvo model 2003, engine is approx 25 years old. Has started to put out white smoke with unburnt diesel in the exhaust. It is not going through coolant and the oil appears clean so i dont think it is a headgasket or anything related to that. After changing all the filters and no improvement i decided the test the individual cylinders by opening the fuel pipe nut at the injector to see if all the cylinders where firing properly. When i did the test to the first and third cylinders the engine ran really rough and nearly died but when i tried it on the 2nd cylinder the engine did not change. I did these individually and allowed the engine to get back to "normal" between tests. What is the likely cause of this misfiring? Does it mean its time to call the mechanic to pull the injectors?